Question

Encoding and Decoding PPM image

3 & 4 are parts of question 2

Code for a09q1:

Answer 1

I put the code for the entire project here(a09q2 and a09q1), made some minor changes to a09q1

a09q2.py

from a09q1 import PPM

#to perform deepcopies of objects

import copy

#function to encode image

def encode_img(file_name, file_name_secret, file_name_out):

    original_img = PPM(file_name)

    secret_img = PPM(file_name_secret)

    #check if dimmensions match

    if original_img.height != secret_img.height or original_img.width != secret_img.width:

        raise Exception('Image dimmensions do not match, cannot encode')

    

    #make a copy of the original_img

    encoded_img = copy.deepcopy(original_img)

    #zero out the copied image

    encoded_img.zero_out()

    

    for i,row in enumerate(secret_img.image):

        for j,col in enumerate(row):

            #check if pixel is white

            if col == [255,255,255]:

                #increment blue by 1 if white

                encoded_img.image[i][j][2] += 1

    #write to file

    with open(file_name_out, 'w') as file:

        file.write(encoded_img.magic_number+'\n')

        file.write(str(encoded_img.width) + ' ' + str(encoded_img.height)+'\n')

        file.write(str(encoded_img.maxval)+'\n')

        for i,row in enumerate(encoded_img.image):

            for j,col in enumerate(row):

                for k, color in enumerate(col):

                    file.write(str(color))

                    if k != 2 or j != encoded_img.width-1:

                        file.write(' ')

            file.write('\n')    

#function to decode image

def decode_img(file_name, file_name_out):

    encoded_img = PPM(file_name)

    decoded_img = copy.deepcopy(encoded_img)

    for i,row in enumerate(decoded_img.image):

        for j,col in enumerate(row):

            #check if pixel is white

            if col[2] % 2 == 0:

                decoded_img.image[i][j] = [0,0,0]

            else:

                decoded_img.image[i][j] = [255,255,255]

    #write to file

    with open(file_name_out, 'w') as file:

        file.write(decoded_img.magic_number+'\n')

        file.write(str(decoded_img.width) + ' ' + str(decoded_img.height)+'\n')

        file.write(str(decoded_img.maxval)+'\n')

        for i,row in enumerate(decoded_img.image):

            for j,col in enumerate(row):

                for k, color in enumerate(col):

                    file.write(str(color))

                    if k != 2 or j != decoded_img.width-1:

                        file.write(' ')

            file.write('\n')                    

a09q1.py

class PPM:

    def __init__(self, filename):

        #the image is defined as a 3d list

        #1st dim = row list

        #2nd dim = rbg pixel list

        #3rd dim = color value for that pixel

        with open(filename, 'r') as file:

            data = file.read().splitlines()

            self.magic_number = data[0]

            dimmensions = data[1].split(" ")

            self.width = int(dimmensions[0])

            self.height = int(dimmensions[1])

            self.maxval = int(data[2])

            #validata image height

            if len(data)-3 != self.height:

                raise Exception('Invalid Image {}, height mismatch'.format(filename))

            self.image = []

            for row in range(self.height):

                rowForImg = []

                rowdata = data[3 + row].split()

                #validate image width

                if len(rowdata)/3 != self.width:

                    raise Exception('Invalid Image {}, row mismatch'.format(filename))

                for col in range(self.width):

                    pixel = []

                    for color in range(3):

                        #add color to pixe;

                        pixel.append( int(rowdata[col * 3 + color]) )

                        #validate max val

                        if pixel[color] > self.maxval:

                            raise Exception('Pixel value exceeds max value at row={} col={} filename={}'.format(row,col, filename))

                    #add pixel to row

                    rowForImg.append(pixel)

                #add row to image

                self.image.append(rowForImg)    

            

    def __eq__(self, other):

        if not isinstance(other, PPM):

            return False

        

        if self.magic_number != other.magic_number:

            return False

        if self.width != other.width:

            return False

        if self.height != other.height:

            return False

        if self.maxval != other.maxval:

            return False

        if self.image != other.image:

            return False   

        return True

    def __repr__(self):

        return "Dimmensions: ({0.width}, {0.height})\nImage: {0.image}".format(self)

    def zero_out(self):

        for row in self.image:

            for col in row:

                if col[2] % 2 != 0:

                    col[2] = col[2] - 1

                        

Code Screenshots

a09q2.py

from a09q1 import PPM #to perform deepcopies of objects import copy 3 5 #function to encode image 6 Vdef encode_img(file name, file_name_secret, file_name_out): original_img = PPM(file_name) secret_img = PPM file_name_secret) #check if dimmensions match if original_img.height != secret_img.height or original_img.width != secret_img.width: raise Exception('Image dimmensions do not match, cannot encode'), #make a copy of the original_img encoded_img = copy.deepcopy (original_img) print(encoded_img) #zero out the copied image encoded_img.zero_out() print(encoded_img) for i,row in enumerate(secret_img.image) : for j,col in enumerate(row): #check if pixel is white if col == [255,255,255]: #increment blue by 1 if white encoded_img.image[i][j][2] += 1, #write to file with open(file name_out, 'W') as file: file.write(encoded img.magic number+'\n') file.write(str(encoded_img.width) + ' ' + str(encoded_img.height)+'\n') file.write(str(encoded_img.maxval)+'\n'), for i,row in enumerate(encoded_img.image): for j, col in enumerate(row): for k, color in enumerate(col): file.write(str(color))

if k != 2 or j != encoded_img.width-1: file.write(' ') file.write('\n') #function to decode image def decode_img(file name, file_name_out): encoded_img = PPM(file_name) decoded_img= copy.deepcopy(encoded_img) for i, row in enumerate(decoded_img.image): for j,col in enumerate(row): #check if pixel is white if col [2] % 2 == 0: decoded_img.image[i][j] = [0,0,0] else: decoded_img.image[i][j] = [255,255,255] #write to file with open(file name_out, 'W') as file: file.write(decoded img.magic_number+'\n'), file.write(str(decoded_img.width) + ' ' + str(decoded_img.height)+'\n') file.write(str(decoded_img.maxval)+'\n'), for i,row in enumerate(decoded_img.image): for j, col in enumerate(row): for k, color in enumerate(col): file.write(str(color)) if k != 2 or j != decoded_img.width-1: file.write(' ') file.write('\n')

a09q1.py

1 class PPM: def init__(self, filename): #the image is defined as a 3d list #1st dim = row list #2nd dim = rbg pixel list #3rd dim = color value for that pixel with open(filename, 'r') as file: data = file.read().splitlines() self.magic_number = data[@] dimmensions = data[1].split("") self.width = int(dimmensions[0]) self.height = int(dimmensions[1]) self.maxval = int(data[2]) #validata image height if len(data) -3 != self.height: raise Exception('Invalid Image {}, height mismatch'.format(filename) self.image = [] for row in range(self.height): rowForImg = [] rowdata = data[3 + row].split() #validate image width if len (rowdata)/3 != self.width: raise Exception('Invalid Image {}, row mismatch'.format(filename) for col in range(self.width): pixel = [] for color in range(3): #add color to pixe; pixel.append( int(rowdata[col * 3 + color])) #validate max val if pixel[color] > self.maxval: raise Exception ('Pixel value exceeds max value at row={} col={} filename={}'.format(row, col, filename)) #add pixel to row

rowForImg.append(pixel) #add row to image self.image.append(rowForImg) def _eq_(self, other): if not isinstance(other, PPM) : return false if self.magic_number != other.magic_number: return false if self.width != other.width: return false if self.height != other.height: return false if self.maxval != other.maxval: return false if self.image != other.image: return false return True def_repr__(self): return "Dimmensions: ({0.width}, {0.height})\nImage: {0.image}".format(self) くくくく def zero_out(self): for row in self.image: for col in row: if col[2] % 2 != 0: col[2] = col[2] - 1